I don't like using Vignettes, but I do like doing what Athena Carey calls a "tonal squeeze." In this technique, one darkens the top and the bottom edges (areas) of the photo, but one leaves the sides unmodified. By this technique, the eye is not confined by the sides of the photo, but the darkening of the top and bottom of the photo holds the eye back from leaving at the top or the bottom.
My problem is that I can't figure out how to do this in Affinity Photo. My experiments have so far failed me.
Can anyone help?